This post comes to us from Dr. Bob Dziak:
Even though ~75% of Earth’s volcanic activity occurs below the sea surface, many questions remain on the longevity and acoustic characteristics of explosive seafloor eruptions. To date, only two active eruptions have ever been observed visually in the deep-ocean (>500 m) volcanoes, and then only over time periods of hours to days. The discovery of the actively erupting West Mata volcano in the NE Lau Basin near Samoa (Fig 1) offered a rare opportunity to investigate a deep-ocean, explosive eruption. Video images of West Mata collected by remotely operated vehicle (ROV) provided unprecedented details on the dynamics of gas-driven eruptions at 1200 m depth.
In his recent paper, Dziak et al  present the unique acoustic signatures of West Mata’s two erupting summit vents, called Hades and Prometheus.
To see a video of West Mata erupting under the ocean and for more information on this publication, visit AGU’s Blog.
During its eruption phase, Hades exhibited spectacular 1-2 meter diameter gas filled bubbles of lava (Fig 2) that produced distinctive short duration low frequency sounds when they burst. Prometheus exhibited long duration (1-5 minutes), violent explosions that produced broadband sounds that sometime develop harmonic tones within the explosion record. Over a 6-month period while the hydrophones were recording, the eruption activity at West Mata declined and eventually ceased, allowing us the first view of the demise of a multi-year eruption cycle of a deep-ocean volcano. This paper also provides the background for future work to use these acoustic records of the West Mata to estimate the amount of magmatic CO2 gas that was expelled into the ocean during the eruption.